The present invention relates generally to ion implanters, and more specifically to a contaminant collector trap for such ion implanters.
Conventional ion implantation systems, used for doping workpieces such as semiconductors, typically include an ion source that ionizes a desired dopant element that is then accelerated to form an ion beam of prescribed energy. The ion beam is directed at the surface of the workpiece to implant the workpiece with the dopant element. The energetic (generally positive) ions of the ion beam penetrate the surface of the workpiece so that they are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity. The implantation process is typically performed in a high-vacuum process chamber which prevents dispersion of the ion beam by collisions with residual gas molecules and which minimizes the risk of contamination of the workpiece by airborne particulates. Other portions of the ion implanter, including the ion beamline through which the ion beam passes, are also evacuated.
High-powered turbo pumps or roughing pumps typically provide the required vacuum conditions in ion implantation systems. As shown in the prior art system 10 of FIG. 1, such systems often include a roughing pump 12 for evacuating a chamber defined by the ion implanter terminal 14, which contains a high voltage gas box 16, an ion source 18 and a mass 20 analysis magnet 20. As is known in the art, gas provided by the gas box 16 is ionized in the ion source 18 and extracted in the form of an ion beam 22. The ion beam 22 is mass analyzed by the mass analysis magnet 20 and output from the terminal 14 through terminal aperture 24.
The high voltage gas box 16, which typically operates at a voltage significantly higher than the terminal voltage, is electrically isolated from the terminal 14 by insulators 26. The terminal is electrically isolated from an implanter enclosure 28 by insulators 30. The implanter enclosure 28 is situated at electrical ground potential.
The roughing pump 12 evacuates the interior of the terminal 14 via an inlet (not shown or designated), and outputs any evacuated gases, liquids or particulates via its insulated outlet 32 into the terminal main exhaust duct 34. In addition, the exhaust duct 34, which is electrically grounded along with the implanter enclosure 28, is used to vent the high voltage gas box 16 to the external environment. As such, the exhaust duct includes an insulative (e.g., plastic) extension 36 that connects the gas box 16 to the implanter enclosure 28 through the terminal 14.
A problem with the pump evacuation system shown in FIG. 1 is that gaseous matter pumped out of the terminal passes through phase changes caused by temperature loss and tends to condense on the walls of the exhaust duct 34 above the terminal. In addition, toxic fumes evacuated by pump 12 react with the cooler extraction flow in the terminal exhaust duct 34 to form an acidic liquid (e.g., hydrofluoric (HF) and phosphoric (PF) acids). Over time, these liquids accumulate until the quantity is sufficient to sublimate tracking down the plastic extension 36 by what could be described as a capillary pumping action. The liquid provides a conductive path between portions of the implanter residing at significantly different voltages, thereby presenting a risk of arcing or other electrical discharge through the extension 36. In addition, the liquid may corrode the gas box 16.
One solution to this problem is to provide additional heated gas (e.g., nitrogen or air) into the inlet or outlet of the pump to keep the corrosive contaminants suspended in the exhaust gases to thereby prevent condensation of these acidic liquids. However, such additional gases reduce the efficiency of the pump and may cause it to shut down if appropriate pump pressure sensors indicate an overpressure condition.
Another solution is to provide a filter trap or water-cooled collector in the exhaust duct 34 for trapping or collecting the liquids condensing therein. However, the addition of such traps or collectors reduces the exhaust gas flow through the exhaust duct 34 and may again cause the pump to shut down if an overpressure condition is indicated by appropriate pump pressure sensors.
It is an object of the present invention, then, to provide a mechanism for separating liquids and gases which are evacuated from a chamber by a pump. It is a further object of the invention to provide a mechanism for evacuating a chamber by a pump wherein the risk of electrical discharge or arcing is minimized. It is yet a further object of the present invention to provide a pumping system wherein condensing liquids are prevented from posing the risk of corrosion or electrical discharge. It is a still a further object of the invention to provide an easily maintainable system for removing evacuated liquids in a vacuum system.
An evacuation system for a chamber is provided, including a pump for removing gases and contaminants from the chamber. The pump has an outlet connected to an exhaust duct. A collector trap for use in collecting contaminants evacuated from the chamber is positioned between the pump outlet and the exhaust duct. The collector trap comprises: (i) a gas/contaminant separator having an inlet for introducing gases and contaminants therein, the separator functioning to physically separate the gases and contaminants; (ii) a contaminant collector for collecting the separated contaminants, the collector including an extractor coupling for allowing extraction of the contaminants from the collector; and (iii) an outlet for allowing the separated gases to exit the gas/contaminant separator and into the exhaust duct.